Multiple Choice
What is the total number of principal energy levels that are completely filled in an atom of magnesium (atomic number 12)?
3
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10. Periodic Properties of the Elements
The Electron Configuration
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Which of the following electron configurations correctly represents the placement of electrons around a nitrogen atom?
A
1s^2 2s^1 2p^4
B
1s^2 2s^2 2p^5
C
1s^2 2s^2 2p^6
D
1s^2 2s^2 2p^3
Verified step by step guidance1
Step 1: Identify the atomic number of nitrogen, which is 7. This means a neutral nitrogen atom has 7 electrons to place in its electron configuration.
Step 2: Recall the order in which electrons fill atomic orbitals: first the 1s orbital, then the 2s orbital, followed by the 2p orbitals.
Step 3: Fill the 1s orbital with 2 electrons, since it can hold a maximum of 2 electrons: $1s^{2}$.
Step 4: Fill the 2s orbital with 2 electrons, as it also holds a maximum of 2 electrons: $2s^{2}$.
Step 5: Place the remaining 3 electrons in the 2p orbitals, which can hold up to 6 electrons, resulting in $2p^{3}$. Thus, the full electron configuration is $1s^{2} 2s^{2} 2p^{3}$.
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